In recent years, permeable reactive barrier (PRB) is a fast-growing technology used in the in-situ remediation of pollutant in groundwater. It has been widely used, and been gradually regarded as the mainstream technology in this field. Up to now, more than 120 PRB have been settled up in North American and Europe. Currently, the use of high-level oxidants as the filler of PRB for the remediation of pollutant in groundwater has been the spot-light in the PRB field. Among these oxidants, persulfate has been largely used in the removal of refractory organic compounds, and gradually been the hotspot in the in-situ chemical remediation of pollutant, because the persulfate has several advantages as follows: 1. low-cost persulfate can product the sulfate radical (standard oxidation-reduction potential: E0=+2.5˜+3.1V) with strong oxidizing property, under the condition of transition metal catalyst; 2. persulfate presents high oxidization ability in acidic, neutral, and alkaline conditions.
Persulfate with the concentration of ca. 200 mg/L usually presents good degradation effect for the pollutant dyes (such as 2,4-DNT, MTBE) with the concentration of 10 mg/L. However, the solubility of the persulfate in water is in the range 5.3-54.9 g/100 mL, and thus the use of persulfate directly as the filler of PRB can result in the waste of oxidant and secondary pollution of groundwater, and this also cannot maintain long-time degradation effect. Therefore, it is necessary to develop new method to achieve the sustained release of the persulfate toward their high-effective and long-time utilization.
Currently, the most common preparation method of sustained-release materials is mixing the persulfate and adhesive material into bulk substance, in which the persulfate can be distributed uniformly. However, when these persulfate-based sustained-release materials were immersed into water, the released rate is high initially, and then gradually stable, which will be very low during a long time. Therefore, how to achieve the long-time and stable release of the persulfate plays a key role in the design these materials.